Preparation of cyclopentadiene from dicyclopentadiene



Dec. 13, 1949 H. L. GERHART PREPARATION OF CYCLOPENTADIENE FROM DICYCLOPENTADIENE 2 Sheets-Sheet 1 Filed Deo. 5, 1947 /A/a/f'NTO/e H0 WHeDL. GERA/HET Dec. 13, 1949 GERHART 2,490,866'

H. PREPARATION OF CYCLOPENTADIENE FROM DICYCLOPENTADIENE Filed Dec. 5, 1947 2 Sheets-Sheet 2 ll//V Patented Dec. 13, 1949 PREPARATION 0F CYCLITEYNTADIENE FROM DICYCLOPENTADIENE Howard L. Gerhart, Milwaukee, Wisl, assigner to Pittsburgh Plate Glass Company, Allegheny County, Pa., a corporation of Pennsylvania Application December 3, 1947', serial No.'7s9,54s

These and other objects of the invention willbe apparent from consideration of the following specification and claims.

Dicyclopentadiene is obtained in certain hydrocarbon fractions resulting as by-products of municipal gas, coal tar and petroleum idustries. It has a boiling point of about 170 C. and decompcses at the latter temperature into cyclopentadiene, having a boiling point of 42 C. Accordingly, it has been proposed to prepare cyclopentadiene from the dicyclopentadiene by distilling of the latter through a iractionating column. However, this method has not been satisfactory because in the distilling process dicyclopentadiene.

tends not only to decompose, but also to condense or polymerize in order to form compounds whichv do not readily crack or split to form the monomer.`

The reaction is also relatively slow and ineliicient and cannot be used with dilute dicyclopentadiene.

According to the present invention dicyclopentadiene is depolymerized by continuously passing dicyclopentadiene vapors which exert a.

pressure below atmospheric pressure, as hereinafter explained through a conduit such as a pipe which may be in the form of a pipe coil,v

heated above 200o C. at a zone intermediate the ends of the conduit (usually by heating the coil) and removing the cyclopentadiene evolved from the heating zone through the conduit or coil and condensing it before substantial polymerization or further cracking of the dicyclopentadiene or cyclopentadiene can occur. The temperature of heating should not be above the temperature at which serious decomposition of the cyclopentadiene occurs and usually is below about 800 C., frequently being 200 to 600 C.

This heating causes depolymerizationto form y.

However, I have found that cyclopentadiene. poor yields are obtained unless certain precau- 13 Claims. (Cl. 260-666) tions are lobserved. I have discovered, according to this invention that such poor yields may be caused by further cracking of the cyclopentadiene in the ,heatingv zone and also by polymerization of the'cyclopentadiene and dicyclopentadiene either'in the heating zone or in cooler areas of` the' cracking apparatusA prior to condensation.' By rapidly removing the evolved cyclopentadiene fromv the heatingY zone this difticulty is avoided particularly when this rapid removal is accompanied by conduct of the resulting vapor (within several seconds or less) to a condenser capable of condensingevolved cyclopentadiene to liquid state.

15g rThis new process has been found to be highlyl `200 C. in the `manner described above.

successful for the production of cyclopentadiene in yieldswell above 80% and generally at least 90 to: 95% of theoretical.

This process may be conducted with good eect by continuously feeding the dicyclopentadienethrough a conduit such as a pipe of essentially constant diameter and heating the pipe interme diate its ends whereby rapid expansion of gases tends to occur due to the evolution of cyclopentadiene and the'increase in temperature. Becausev free escapeof the vapors from the heating zone is permitted, the expansion of the gases therein c auses a' rapid increase in the rate of movement of the vapor stream as it passes through the heat-- ing zone and thus affords removal of the vapor fromthe heating zone and delivery of the gases to'a condenser (in the matter of not more than afew seconds) at a sufciently rapid rate to in-` hibit polymerization of the evolved product. Ob-

viously the same effect may be obtained if the;

diameter of the `conduit at the exit end of the zone of heating is-'sli-ghtly larger or smaller than the diameter of the .conduit at the inlet end. of the zone, so llong as free escape of the evolved vapors from the heating zone is permitted and the gas expansion in the heating zone tends to cause an appreciable increase in the rate of vapor ow through. the zone.

According tothe fpresent invention, an espe- "cially eective method has been provided which ensures rapid Yremoval of evolved cyclopentadiene from the heating zone. According to this method,-4

dicyclopentadienevapors which exert a pressure'below atmospheric pressure are heated above y Such a process is especially valuable since it prevents establishment of alarge concentration of cyclopentadiene or dicyclopentadiene in the heating zone andV therefore inhibitsl polymerization of either of these compounds, Thus the process may be performed by maintaining the cracking zone under vacuum. Furthermore the process may be conducted in the presence of diluents for example vapors of other liquids which boi1 at the temperature range of the boiling point of dicyclopentadiene and which establish a vapor mixture in which the dicyclopentadiene is present and in which the partial pressure ofthe dicyclopentadiene is below atmospheric.

For a better understanding of the invention reference may now be had to the accompanying drawings in which the Figures il, 2 :and I3 are diagrammatic views illustrating respectively an assembly of apparatus for use in .practicing the invention; a modiiied form of -absorbingapparatus for taking up cyclopentadiene .as;it-is formed; a form of the apparatus including a slightly modiiied type of converter for pyrogenetically changing dicyclopentadiene into cyclopentadiene and Fig. 4 is a diagrammatic view of a further assemblage -which may be used in the performance of this invention.

In the drawings like numerals refer parts throughout.

The apparatus as shown in Figure 1 vincludes three sections 8, 9, and l0, enclosed `for `purposes of clarity, by dotted lines. Section B includes apparatus for pyrogenetic treatment .of .-dicyclo.- pentadiene, e. g. a suitable tower Il, the bottom portion of which may be packed with a porous or granular material l2 such as fragments Aor rings of carbon, or steel chips or .shavings, .fragments or rings of porcelain oranyother material which will provide a suitable non-reactive foraminous packing. Dicyclopentadiene is supplied to the tower at a regulated rate of .,ow from .a reservoir i3, which is connected to the tower by a line It. Heat is supplied to the treating column or chamber by any suitable means, e. g., by means of electrical `resistance element 16., appropriately coiled about the exterior-.of the chamber.

The vaporous products from -the chamber of column Il are discharged at `the-bottomof the latter through a line l1, -to apparatus 9 .that includes appropriate means for `-eiecting separation of cyclopentadiene ifrom any `unconverted dicyclopentadiene. The latter apparatus vto like as shown in Figure l includes aa condenser .ofv

conventional design involving a shell or column i8 through which extends a 'condenser VVcoil L9 joined at its upper end to line -l'L Cooling fluid is admitted to the shell through aligne :2l and discharges through line 2,2. vCondensed pledutts are discharged from the lower extremity of the coil I9 by means of aline 23 into a Still 2 4, .the temperature of which isappropriately contr..0l1 ed by conventional means (not shown) Such1as -a coil for heating or cooling iluid. In the still, cyclopentadiene is vaporized, `while any -dicyclopentadiene is retained in liquid phase .and isdischarged from the bottom of the still through a line 26 leading to a pump 21, that -recycles `Vit through line 28 to the feed line I4. .If.preferred, dicyclopentadiene may be discharged lto an appropriate receiver through aline 29. Valves `3i! in lines 2B and 29 provide means for controlling the discharge of recovered dicyclopentadiene.

Cyclopentadiene, in vapor form, `is discharged from the still through line 3l lextending to receiver apparatus l0.

to the line 3l. is connected to a line 34 extendingdownwardly lThe apparatus shown in Fig.1 includes a condenser column 32 ythrough-which.Y extends a coil 33 connectedat its upper extremity At the lower extremity, the coil and discharging adjacent to lthe bottom of a re` ceiver 3S is lilled to an appropriate level with an absorption liquid. Vapors of cyclopentadiene bubble upwardly through the liquid and those not absorbed in receiver 36 are discharged at the top thereof through a conduit 3T that extends downwardly almost to the bottom of a second receiver 38, which likewise is appropriately filled with absorption liquid. Liquid within the receivers 36 and 38 may be cooled to optimum temperature for absorbing cyclopentadiene by means of cooling coils 39 and 4l connected in series by conduit 2 and being respectively provided with inlet 4,3 and outlet de. The absorption chamber '38 is also provided at its upper extremity with Aaline 46 leading to a suitable source of vacuum (not shown) by means of which the entire system is maintained under an appropriate degree of vacuum.

If preferred, the vapors from the converter ll need not be condensed in condenser I8. Instead thecondenser maybe by-passed by means of line 41 directly connecting the line I'i with an appropriate portion oi the still 24. The latter may then be operated as a flash tower in which the relatively high boiling dicyclopentadiene is condensed while the relatively volatile cyclopentadiene passes ol as a vapor through line 3l to absorber lil. Oi course lines -l'l and 41 are provided with suitable valves t8 by means of which the path of the vapors can be controlled or determined at will.

Fresh absorption liquid or solvent may be admitted to either receptacle 36 or 38 through inlets 47a. and charged absorbent liquid may be drawn off by vacuum through outlets 68a. The two containers are also interconnected by line 49 for countercurrent orrconcurrent flow of the solvent.

In Figure 2 is shown a modiiied form of absorber for cyelopentadiene which is indicated in general by the numeral 5B. The unit may be substituted bodily for the unit l@ disclosed in Figure 1. It includes a tower or absorption column 5l into the bottom of which a line 52 connected to line 3|, from still 24 discharges cyclopentadiene vapors. For purposes of cooling the absorption medium the absorption column is also provided with a discharging conduit or line 53 leading to a pump 54, which discharges through line 5E or optionally to an outlet line 5T, leading to a suitable storage receiver or to a cooling coil 58, in a cooling column 59 provided with inlet and outlet conduits 6i and 62, through which a suitable cooling medium may be circulated. The coil 58 is connected to discharge cooled fluid through conduit 63 into the upper extremity of the absorption column 5l. The system is maintained under vacuum `by means of conduit 64 leading to a suitable vacuum pump (not shown). Fresh solvent is added through line 65.

A second form of pyrogenetic treating unit which may be substituted for the unit 8 is shown in Figure 3, and includes a column 6l, the bottom portion of which is appropriately packed with carbon rings or lumps o1- steel chips or shavings, or any other suitable packing material. The zone of the column containing the packing is heated by means of a resistance coil S9. Vapors of dicyclo-pentadiene are discharge upwardly through the packing material through a line 'H i .supply of dicyclOpentadiene. The upper portion of the column is provided with a condenser coil 'I5 having inlet 'I6 leading to a suitable source of cooling fluid such as water, and an outlet 'I'I leading to some convenient means for disposing of the warm fluid.

Undecomposed dicyclopentadiene passing upwardly through the packing in the column is condensed by the coil and is collected and recycled to the still 'I2 by a conduit 'I8 connected to an intermediate portion of the column. If preferred the condensed dicyclopentadiene may be discharged to storage by conduit 19, which is connected to line 78. Valves 8| in the lines 18 and 'I9 provide means for determining the course of ow of the condensed liquid.

The vapors consisting essentially of cyclopentadiene are discharged from the top of the column through line 82 leading to an absorption system which, as shown in the drawings, substantially corresponds to the system I0 shown in Figure 1. Of course it will be apparent that the absorption apparatus 50 disclosed in Figure 2 may be substituted in lieu thereof.

The point of inlet of the dicyclopentadiene into the system is optional. For example, it is quite possible to charge it through a line 84 to the bottom of the column 61, or if preferred, it may be charged to intermediate portions of the column through lines 86, or to the top portion through line 8l. The dicyclopentadiene will then be vaporized in the column, or in event that it is not at once vaporized, it will return backwardly through line 'II or line 'I8 to the still l2 where it will be vaporized and permitted to pass upwardly through the packing in the column 61.

In the operation of the apparatus disclosed in Figure 1, dicyclopentadiene from the container I3 is fed downwardly through conduit I4 into the cracking column I2 which is suitable packed with carbon rings or steel lings or the like. The lower portion of the column which constitutes the cracking zone is maintained at a temperature above about 170 C. and preferably within a range of about 200-3000 C. The latter temperature may sometimes be exceeded and may even be as high as 800 C., but in general it is preferable not to do so. In any event the temperature should not be so great as to cause excessive charring vof the charge, or to cause vapors to be discharged from the still at such temperature and rate as to carry over an excessive amount of uncracked or unchanged dicyclopentadiene. The system is evacuated through the conduit 46, and preferably the pressure (absolute) within the system is at least 50 millimeters below the pressure of the surrounding atmosphere usually within the range of about to 600 mm. of mercury, a good average operating pressure being approximately 1/2 atmosphere.

Vapors of cyclopentadiene admixed with some dicyclopentadiene pass from the cracking Zone through conduit I1 into condenser` coil I9, where the latter vapors, along with some of the former, are condensed and run down into the still 24. In the still, the cyclopentadiene is maintained in or converted into vapor phase and passes olf through line 3|. The latter, if desired, may be of such length or may be provided with cooling means in order to impart thereto a certain degree of refluxing action to assist in the thorough separation of any dicyclopentadiene carried in the vapors. Dicyclopentadiene is withdrawn from the bottom of the still through line 26 and is returned by pump 21 to feed line I4.

If preferred the dicyclopentadiene may also be withdrawn to storage through line 29.

Cyclopentadiene vapor passing off through conduit 3| is conducted to absorption apparatus I0 shown in Figure 1, or to apparatus 50, shown in Figure 2. Assuming it is conducted to the former, the vapor passes downwardly through condenser coil 33, maintained at an appropriate temperature. The coil then discharges into receiver 36 filled with an absorbent medium such as Xylol, tung oil, soya bean oil, linseed oil or other vegetable oil. Any vapors not absorbed pass over through line 3l into absorber 38. Assuming that the system is at a pressure of about 1/2 atmosphere and that the absorption liquid such as xylol or the like within the receivers 36 and 38 is at a temperature of zero degrees C., a concentration of 50% cyclopentadiene in xylol can readily be obtained.

Where oils are employed as absorbents, the mixture may be subjected to polymerization by heating to 50 C. or thereabout in the presence of 2 or 3% of a catalyst, such as luoboric acid. The product is probably a joint polymer of the hydrocarbon and the oil. Details of polymerization of cyclopentadiene in a glyceride oil are disclosed in my copending application entitled Resinous material, Serial No. 324,392, filed March 16, 1940, now United States Letters Patent No. 2,398,889, granted April 23, 1946.

The absorbers 36 and 38 may be filled through lines 47a. and then operated until the liquid is suflciently saturated, after which the liquid is drawn off for separation of the cyclopentadiene by distillation. It is also possible to make additions of solvent continuously or in small amounts at short intervals and to make corresponding withdrawals of charged solvent at outlets 48a. If preferred, counter-current flow may be obtained by charging fresh solvent into receptacle 38, transfer of solvent from one receptacle to the other being effected through line L49. Likewise, the flow may be reversed or made concurrent by making additions of fresh solvent to receptacle 33 and withdrawals from receptacle 36.

As already stated, condenser I9 may be eliminated and the still 24 operated as a flash tower. In the latter event the valves 48 are operated to effect the passage of the vapor products from column I i through conduit 4l directly to the still. The still is then maintained at such temperature that the cyclopentadiene passes on through line 3 I, while the unchanged dicyclopentadiene is condensed and again recycled through line 26 and pump 21 to the cracking column II.

Regardless of whether the column 24 is operated as a still to effect distillation of cyclopentadiene from dicyclopentadiene condensed in coil I9, or as a flash tower directly receiving the products from the column I I, it will be apparent that recovery of the cyclopentadiene, by absorption in xylol or other solvent, may be effected in either the apparatus I0, as shown in Figure 1, or in the apparatus 50, as shown in Figure 2.

In event that the apparatus shown in Figure 2 is employed for absorption of cyclopentadiene, the vapors are discharged through line 3l to line 52, which then feeds them into the bottom of tower 5I. Xylol or the like absorbent in the tower flows out through line 53 and is forced upwardly by pump 54 through line 56 to cooler coil 58. It returns through line 63 to the top of tower 5I and is thus maintained in counter-current flow in the latter. Additions of fresh absorbent are made through line 65 and corresponding withdrawals are made through line 51.

In the operation of the cracking apparatus disclosed in Figure 3 dicyclopentadiene may be charged into the still 'l2 where it isboiled at a subatmospheric pressurev for example, a pressure of about 1/2 atmosphere and the vapors pass upwardly into the cracking column 6l, where they are subjected to a cracking temperature, for example, about 20G-300 C. The vapors of cyclopentadiene and uncracked dicyclopentadiene and any impurities contained therein pass into the upper part of the column Where they are cooled by the coil 'l5 to such degree as to condense the dicyclopentadiene and the impurities. The monomer passes on through-the conduit 82 to the ab` sorption apparatus. The dicyclopentadiene and the impurities are returned to the cracking zone or else are carried by the conduit '|8 back to the still 12. Direct return of the unchanged material may be assisted by causing the pressure to surge over a range of about 50 mm. at 30 second intervals.

If preferred, dicyclopentadiene may be charged directly into the column 6l. Admission may be eiected at any one of the points 84, 85 or 8?. If the material is introduced at the former point it is converted into vapors which pass upwardly through the packing Within the column. If it is introduced at the top of the column the cold liquid helps to reduce or control the temperature of the reaction Zone. cyclopentadiene vapors when properly separated from dicyclopentadiene vapors can be dra-wn ol at the top of the still or column Sl through column 8.2, or if preferred from the line 'i8 and line 19. Recovery of the cyclopentadiene may be effected by conducting the vapors through absorbing units Ill or 50.

The apparatus is capable of effecting substantially 1.00% conversion of dicyclopentadiene into cyclopentadiene. The process is substantially continuous and the rate of charging may be relatively high and is limited only by the size of the cracking zone and the capacity of the apparatus employed to separate cyclopentadiene from unchanged dicyclopentadiene.

In order to demonstate eiiiciency and high capacity of the apparatus for converting the dimer of cyclopentadiene into the monomers, 204 parts of an 80% solution of dicyclopentadiene were charged into a round bottomed glass ask equipped with a lagged fractonating column. The flask was heated to boiling and the cyclopentadiene as it evolved was condensed in a receiver chilled by dry ice. In three hours 144 parts of cyclopentadiene were collected. Any attempt to hasten the cracking operation by vapplying more heat to the still resulted in the dicyclopentadiene distilling over.

For purposes of comparison, an apparatus of the design shown in Figure 1 was fed by continuous flow over a period of 4 hours with 1678 grams of dicyclopentadiene solution similar to that above described. The pressure in the cracking column i was maintained at 380 mm. and the temperature of the cracking Zone was maintained at 309 C. at the top and 325 C. at the bottom. The condenser |`8 was maintained at a temperature of '72 C. and the absorption chambers 36 and 3B were maintained at zero degrees C. Absorption was continued until the. concentration of cyclopentadiene in the xylol employed as an absorption medium was 60%. In` this Way a total of 1,112 grams of cyclopentadiene was absorbed. The liquid from the still 2li was recycled to obtain a additional yield of cyclopentadiene. Dicyclopentadiene may be replaced by dicyclohexadiene to produce hexadiene.

To perform a further series of experiments, an

apparatus illustrated in Fig. 4 was erected. This apparatus comprised a still |90 connected `to the lower end of a vertically mounted tube |02, 6 .feet in length and two inches in diameter. The lower half of this tube was wrapped with a heating coil |04 which was provided with a rheostat |06 and was connected to a source of potential (not shown). Means for measuring the temperature within the heating zone was provided by disposing three thermocouples |28, |30 and |32 in the bottom, middle and top respectively of the heating zone.

The upper portion of the tube was provided with a cooling jacket |08 which eiiected a precooling and condensation of dicyclopentadienc from the cyclopentadiene. The tube |02 was provided with an outlet line Hc to convey evolved vapors rapidly to condenser ||2 which was connected at its lower end to a receptacle H4. The tube |02 also Was provided with a conventional collector (not shown) for collecting any condensate (dicyclopentadiene) which news down the walls of the tube from the jacketed portion thereof and for delivering such collected condensate to the still lili) by way oi lines |22 and |20. Receptacle H was connected to still |90 by line |20 and the lines |22 and |20 were provided with suitable valves |24, |26 and |21 for regulating flow therethru.

Receptacle lli was provided with an outlet I8 which was connected to a cyclopentadiene condenser and also to a vacuum pump. This receptacle also had an inlet ||8 for introduction of dicyclopentadiene into the system.

In the operation of this equipment dicyclopentadiene was introduced through inlet ||8 and allowed to flow into the still. closed and the still Was heated to vaporize olicyclopentadiene. The vapors passed upwardly through the heating zone, were partially cooled in the upper jacketed portion of the tube and further cooled in condenser ||2 to condense out dicyclopentadiene and certain high boiling impurities if present and to deliver this material to the receptacle H4. Cyclopentadiene vapor passed on through line H6 and immediately to a Water cooled condenser where the cyclopentadiene Was condensed. Thus the evolved cyclopentadiene was condensed within a very short time (not more than 5 to 10 seconds) after leaving the heating zone.

Temperature of heating zone:

Bottom C 345 Top C 250 Absolute pressure millimeters of mercury 230-240 Charge of technical dicyclopentadiene grams 500 Yield of cyclopentadiene do 390 Percent of theoretical yield per cent" 97.5

In a further test using pure dicyclopentadiene and similar apparatus to that shown in Fig. 4, 30 cc. of Russian mineral oil were introduced into Valve |26 wasy "the still and other conditions of operation were Vas follows:

Recourse to subatmospheric pressure as above 'described permits the contemplated depolymerization to occur in high yield and without production of excessive amounts of undesirable byproducts. These advantages appear to be attained for a number of reasons. First, the use of a subatmospheric pressure permits vaporization of dicyclopentadiene at temperatures below its 'normal boiling point and tendency for polymer formationv is minimized. Further, molecules of dicyclopentadiene and cyclopentadiene are dispersed so that likelihood of contact therebetween in the cracking zone or before condensation is reduced thus reducing possibility of polymer formation. Moreover use offsubatmospheric'pressure facilitates rapid removal of the vapors to the condensing system. Any convenient method of cracking dicyclopentadiene vapor which exerts a pressure below atmospheric is within the contemplation of this invention. While such a vapor pressure may be eiectively established by imposing a subatmospheric pressure upon the system other methods may be resorted to in order to achieve the objects herein contemplated.

Thus, as shown abovethe cyclic diene hydrocarbon may be diluted with substantial, for example, equal volumes of petroleum hydrocarbon or other diluent, boiling below about 170 C. (the boiling point of dicyclopentadiene) particularly those boiling within a range of 160 to 180 C. It will be apparent that the use of such inert or nonreactive diluents results in distillation of a mixture of the diluent and the dicyclopentadiene, which mixture enters the cracking zone. It will be equally apparent that even when the dicyclopentadiene-inert diluent vapor mixture exists at atmospheric pressure, the partial pressure'of the dicyclopentadiene will be less than atmospheric pressure. Consequently use of an inert diluent which distills with the dicyclopentadiene permits recourse to higher pressures and it has been found that the process may be conducted with good yield at atmospheric pressure in such a case.

Various diluents are permissible so long as they distill with the dicyclopentadiene and thereby permit establishment of a dicyclopentadiene partial pressure below atmospheric pressure. Quite commonly technical grade dicyclopentadiene contains other hydrocarbons which have boiling points approximating that of dicyclopentadiene. This is particularly true of dicyclopentadiene which has been prepared by cracking of natural gas or of petroleum oil rening gases. Such products contain dicyclopentadiene mixed with homologues and alkyl substitution products thereof, coumarone, indene, etc., and may also contain some benzene and/ or toluene. Such technical mixtures may be treated as herein described without use of further diluents. Moreover, other diluents such as various hydrocarbons (whether miscible or immiscible) which distill with dicyclopentadiene and therefore cause establishment of a dicyclopentadiene partial pressure below that 10 of the atmosphere (preferably at least 50 millimeters below) may be used. Nonreactive gases such as lcarbon dioxide, natural gas or nitrogen also'may be used.

High boiling diluents, such as those boiling in the range of the dicyclopentadiene boiling point n'and frequently found in technical grade dicyclopentadiene or others boiling above cyclopentadiene are separated by fractional condensation from evolved cyclopentadiene in a condenser such 'as diagram'matically illustrated in Fig. 4 (condenser IIZ) ofthe drawings. Consequently, the 'condensed cyclopentadiene may be obtained in a highly pure state (above and essentially free from impurities present in technical grade dicyclopentadiene.

Although the present invention has been described with reference to specific details of certain embodiments it is not intended that such details' shall be` regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims. This'application is al continuation in part of my copending application Serial No. 324,391, filed March 16, 1940, now abandoned.

I claim: A

1. A process as defined in claim 3 in which the cyclopentadiene is absorbed in a hydrocarbon solvent.""l

2. Al process as defined in claim 3 in v'which the cyclopentadienevis absorbed ina vegetable oil.

.3. A process of preparing cyclopentadiene fromv dicyclopentadiene which comprises continuously passing dicyclopentadiene into a cracking vzonel at a temperature of about to 300 C. and under a pressure of 'about 25 to 500 mm. of mercury, to obtain a vaporous mixture of cyclopentadiene and dicyclopentadiene, continuously withdrawing the vaporous mixture from thecracking zone, condensing out the dicyclopentadiene and absorbing the cyclopentadiene in a solvent medium.

4l `A process of preparing cyclopentadiene from dicyclopentadiene," which comprises continuously passing` vapors of dicyclopentadiene into a cracking zone at a .temperature of about 170 to 300C. and at a pressure within the range of about 25 to 500 mm. of mercury Yto crack the dicyclopentadiene and form a vaporous mixture of cyclopentadiene and dicyclopentadiene, removing a corresponding amount of vaporous mixture from the cracking zone, subsequently condensing out theA dicyclopentadiene and recycling it and absorbing the cyclopentadiene in a solvent medium.

v5. A process ofpreparing, cyclopentadiene from dicyclopentadiene, which comprises continuously passing dicyclopentadiene in vapor phase into a cracking zone at a pressure not above 500 mm. and at a. temperature of 200 to 300 C., removing the resultant mixture of cyclopentadiene and dicyclopentadiene vapors from the cracking zone by causing them to pass upward, condensing out the dicyclopentadiene and returning it to the cracking zone, the return of the condensed dicyclopentadiene being assisted by causing the pressure in the cracking zone to fluctuate.

6. A process of preparing cyclopentadiene from dicyclopentadiene, which comprises continuously passing vapors of dicyclopentadiene into a cracking zone at a temperature of about 170 to 300 C. and at a, pressure within a range of about 25 to 50.0 mm. to crack the dicyclopentadiene and form a vaporous mixture of cyclopentadiene and dicyclopentadiene, removing a corresponding amount of vaporous mixture from a cracking zone, conl1 @lensing out thedioyclopentadiene from the mixture and recycling- 'it-.and absorbing .thecyolopentadiene in the drying ,glyoeride oil `to provide a mixture suitable for copolymeriza'ton into aresinous body.

'I'. 'Process for producing cyclopentadene from dicyclcpentadiene which comprisescontinuously passing a stream of superheated vapors of dicyclopentadiene under subatxnospheric pressure through .a depolymerization zone maintained at a temperature Withinthe range between 200 C. and .30.0 C., `and removing .from such zone the re- .Sultant uyoiopentadiene sufficiently rapidly that substantial .further polymerization of the d iyclopentadiene is inhibited.

8. A process of producing cyclopentadiene from diolclonentadiene which comprises continuously passing e, stream -Aof superheated vapors of dicyciopentadiene under Asubatmospheric pressure through a depolymerizaton zone maintained at L a temperature above 200 C and belowthe temp erature at which substantial decomposition of the .cyclopentadiene voccurs .and removing from slloh zone the resultant cyclopentadiene Suiciently rapidly that substantial'further polymerization of the dicyclopentadiene is inhibited.

9. `A proces-s of producing vcyolopenta.diene from dioyolopentadene which comprises vaporiz'ing dicyclopentadiene at a temperature below the boiling point at normal atmospheric pressure,

continuously passingthe dicyclopentadiene thus formed through a depolymerization zone maintained under subatmosphericpres-sure at .a tem-v perature of at least 200 .C. and below the temperature at which ysubstantial. decomposition of the cyclopentadiene .occurs and removing from such zone the resultant cvclopentadiene .suiiiciently rapidly that substantial `further polymerization .of the dicyclopentadiene is inhibited.

10. A process of producing c yclopentadiene sure substantially to .the-boiling point of dicyclopentadiene at said pressure, continuously passing the vapors of dicyclopentadiene thus formed which vapors lexert a subatmespheric pressure through La. zone-of depolymerization maintained at a, temperature above I200" C. -vand below the temperature- A`at which decomposition of cyclopentadiene occurs and removing the resultant leyclopentadiene sumc-iently rapidly that substant- :tiai further polymerization-of the d-icyclopenta.- diene vis inhibited.

.12. A process of producing cvcldpentadiene from dcyclopentadene which comprises conti-nuously passing astream of vapors fof dioyolopentadiene, which vaporsexert a .subatrnospheric pressure, through a .depolymerization zonemai-n- .tained .at a temperature above 20.0 C. and .below the temperatureat Whichsubstantial desem-posi, tion .of the .cyclopentadiene occurs vand removing from ,such zone the resultant cyclopentadiene suiiicientl-y rapidly .that further polymerization of the .dicyclopentadiene is inhibited.

13....A method .of preparing -cyclopentadiene which comprises .continuously passing a stream of vapors` of dicyclopentadiene and .impurities boiling inthe same range with cyCIopentadiene, which vapors of d-icyclopentadiene exert a subatmospheric pressure, througha conduit, vheating the conduit at a `.zone intermediate the .ends thereof above 200 LC, Yand below 80.0 C. whereby dicyclopentadiene is cracked. and asubstantial Volume increase 0f the vapors deems and causes an increase in the rate of vapor-.flow .thro-ugh .the conduit, and permitting free escape yof fsuch vapors "through the conduit at .the increased rate of `iovv to a zone of lower temperatura whereby cyclopentadiene formed is removed .from the heating zone and condensed before substantial polymerization'of the cyclopentadiene can occur..

HOWARD L. GERHART.

REFERENCES CITED `The ollowing references are of 'record in the ile '.of patent:

UNITED STATES PATENTS Number Name Date 2,1965363 Robertson Apr. -9, '1940 2,211,038 Ward Aug. 13',`l1940' OTHER "REFERENCES Harkness et al., Jour. Chem. Physics, vol. l5,' 684-7 (1937),.

Schulze, Oel KohleErdoel Teer, vol. V14, 113-117 

